Front Flip Animation Bones Rotate After A Certain Degree
For the moment from frame 56 to 64, the root bone goes from 146° to 70°, so your character is flipping back. You need to make the bone rotate from 146 to 250 then 360° for example.
Also, it's better to create a root bone that is completely independent, at the bottom of the character, and not use the spine as the root. Instead parent the spine to the root you've created.